The public are becoming increasingly aware of the risks of the ionising radiation used in medicine. When used responsibly, the potential benefits of x-rays and scanning will outweigh any small risk, and it's important that we should maintain a sense of proportion when assessing the risks of radiation in any context, whether we're having a scan at the local hospital or considering moving to a house next to a nuclear power station
Let me show you why that sense of proportion is important. When asked to rank various hazards in order of the threat to their wellbeing, the public rated the nuclear industry at the top of the list, ahead of smoking, alcohol, chainsaws and … handguns. Now look at the pie chart below. It shows the various sources of radiation exposure to the UK population. You’ll notice that nearly half – the red and orange segments – are due to radon (radioactive gas released from the ground and accumulating in our houses) and ‘other’ background radiation, which includes gamma rays from space and radioactivity from the rocks in the ground. There is nothing we can do to reduce this element of the total exposure, short of changing the specifications of our housing stock to exclude more of the radon (or moving to a different part of the country – see below).
But now look at the blue, purple and violet segments. Again, these constitute nearly half of our annual population exposure and they are all the result of medical imaging procedures. This is why we are so careful to keep doses to a minimum in our radiology departments, and only carry out procedures where the small risks from the radiation are greatly outweighed by the likely benefits of making a diagnosis and prescribing the appropriate treatment. The good news is that, despite the increasing uses of diagnostic imaging, it still accounts for less than the annual dose from background radiation, which we tend not to even consider, let alone worry about.
But what about the nuclear industry that so exercised the minds of the public in the survey quoted above? Well, just to the right of the yellow slice of pie is a grey segment – no more than a line – which represents all sources of industrial exposure, including nuclear. Which is why I said that a sense of proportion is important.
(Remember that these are all population as opposed to individual exposure levels – if you are a supremely fit person who has never been near an X-ray department, your pie chart will look very different from that of a patient who has suffered a lot of illness and had multiple CT scans to follow their response to treatment).
But how much radiation are we talking about?
Well, not very much. Our average exposure in the UK is about 2.7 milliSieverts per year, and this site gives some helpful figures on the relative doses from various medical and non-medical sources. Background radiation varies across the country, and you’ll note that levels in Cornwall are higher than in the rest of the country, due to the composition of the underlying rocks.
And while all of the talk tends to centre on the possible adverse effects of radiation, especially the potential to cause cancer, it’s worth noting that there’s good evidence that small doses may actually protect against it, and provide other health benefits, an effect known as radiation hormesis
A little of what you fancy…?
So radiation can be good for you – really? Well perhaps. Look at the map of background radiation levels for the USA below. Background levels of radiation are over three times higher in the red, mountainous, states than in the blue areas around the Gulf of Mexico. The yellow and green areas are intermediate. However, if you look at a similar map showing the incidence of cancer in the corresponding areas, it’s significantly higher in the blue areas than in the red.
Of course, there may be other differences contributing to the apparent protective effect of higher radiation levels in these populations, but no such bias exists in the nuclear shipyard worker study, which compared death rates from cancer and other causes in two separate populations of workers in the same shipyard. One group serviced nuclear powered ships and received annual radiation doses in excess of that received from natural background by their colleagues who only worked on conventionally-powered vessels. Because the two groups did essentially the same work and were drawn from the same surrounding population, the results could not be influenced by the healthy worker effect or any other environmental differences. There was a significantly lower standardised mortality rate (SMR) from cancer and other causes in the occupationally exposed workers, and the higher the dose, the stronger the effect.
Another study looked at the SMR from cancer and all causes in British radiologists (like me!) who are occupationally exposed to low dose radiation, and this showed an almost identical reduction in SMR compared with doctors practising in other specialties where there was no such exposure. Interestingly, if you look at this abstract of the study in question, you will see that it reported that the radiation had NO effect on the health of the radiologists. That’s because the researchers shared the public’s perception that radiation could only ever be harmful, so there was no point looking for beneficial effects!
All of this led the late Professor John Cameron of the University of Florida to suggest that the population of the Gulf states was ‘radiation-deprived’, which is a novel concept for those of us raised to almost instinctively fear radiation. He even suggested a possible experiment, giving a cohort of people living in the low dose areas a radiation source to keep under their beds, bringing their background up to a similar level to that experienced in the mountains of Colorado and Idaho, and then looking at their incidence of cancer over succeeding years. Needless to say, no one has tried this somewhat politically incorrect/socially unacceptable experiment…yet.
But what about all those nuclear disasters?
You’ll be thinking about Chernobyl and Fukushima? They were undoubtedly disasters, and disasters that could have been avoided with better planning and maintenance, but have they resulted in the widely predicted epidemics of radiation-induced cancer?
The Chernobyl meltdown occurred in 1986, and a 2005 report from the United Nations Scientific Committee on the Effects of Nuclear Radiation (UNSCEAR) confirmed that 134 staff working at the plant and assisting in the immediate containment exercise had received very high doses producing acute radiation syndrome, and 28 of these had died. The rest continued to have problems with radiation-induced cataracts and skin disease. Also, because simple measures to deal with the ingestion of milk contaminated with radio-iodine were not taken, there had been an excess of thyroid cancers in young people, with 15 deaths.
However, they concluded: “To date, there has been no persuasive evidence of any other health effect that can be attributed to radiation exposure”. Those inhabitants who refused to move, and remained in the contaminated area around Chernobyl, received doses similar to those experienced when undergoing a CT scan, so not surprisingly, they suffered no radiation-related ill effects. In fact, there was more ill health and premature death in the population that agreed to be uprooted from their homes and relocated in other parts of the country.
At Fukushima, a reactor of an old, obsolete design, situated over a major fault line was subjected in 2011 to an earthquake and tsunami of unprecedented severity. So perhaps not surprising that it fell apart, although even here, there were failures of preparedness and maintenance that could have mitigated the damage. This time, steps were taken to reduce the effects of ingesting contaminated milk, and the UNSCEAR report into the accident concluded that cancer rates in general were unlikely to be affected, and that although a theoretical risk of an increase in the thyroid cancer rate existed, no such increase had been demonstrated. The last time I looked, no one had died from radiation at Fukushima, although there were of course many deaths from the earthquake and tsunami.
Despite the unique features contributing to the Fukushima accident, Angela Merkel, the Chancellor of a country not noted for its frequent earthquakes, cancelled the German nuclear power programme overnight, at a stroke making it impossible to comply with the country's planned contribution to climate control – a catastrophic failure to keep that sense of proportion I talked about earlier.
None of this is to say that we should be complacent about the need to ensure greater safety around nuclear reactors in the future – just making the point that the public (and political) perception of these events as inevitably apocalyptic in nature is not justified.